Ubuntu 15.04 "Vivid Vervet" reached end of life on February 4, 2016. You will need to update to a later version. See https://wiki.ubuntu.com/Releases for further details.
Ubuntu 15.04 "Vivid Vervet" reached end of life on February 4, 2016. You will need to update to a later version. See https:/ /wiki.ubuntu. com/Releases for further details.